Fermentation products, such as ethanol, can be produced from a wide range of renewable feedstocks. These can be classified in three main groups: (1) readily fermentable sugar materials, such as sugar cane (i.e., sugar cane juice and molasses), sugar beets, sweet sorghum; (2) starchy materials, such as corn, potatoes, rice, wheat, agave; and (3) cellulosic materials, such as stover, grasses, corn cobs, wood and sugar cane bagasse. The readily fermentable sugar material contains simple sugars, such as sucrose, glucose and fructose, that can readily be fermented by yeast. In contrast to starchy and cellulosic feedstocks there is no need for prior hydrolysis of polysaccharides such as starch and/or cellulose/hemicellulose.
Readily fermentable sugar materials, such as sugar cane juice and molasses, are used as substrates in, e.g., Brazilian ethanol production. Yeast, such as especially Saccharomyces cerevisiae, is used as the fermentation organism. Often a yeast recycling system is used where up to 90-95% of the yeast is reused from one fermentation cycle to the next. This results in very high cell densities inside the fermentation vat (e.g., 8-17% w/v, wet basis) and in a very short fermentation time. Ethanol concentrations of 8-11% (v/v) are achieved within a period of 6-11 hours at around 32° C. After every batch fermentation, yeast cells are collected by centrifugation, acid washed (e.g., sulfuric acid at pH 1.5-3.0 for 1-2 hours) and sent back to the fermentation vat. Today a chemical defoamer (dispersant) is added during acid wash at a fixed dosage after each cycle and another chemical defoamer (antifoam) is added directly into the fermentation vat automatically (when foam reaches a level sensor) or manually until foam is fully controlled.
U.S. Pat. No. 3,959,175 discloses an aqueous defoamer composition containing liquid polybutene. The defoamer composition can further comprise in part hydrophobic silica and silicone oils.
U.S. Pat. No. 5,288,789 discloses the use of a condensate of alkylphenol and aldehyde that has been polyoxyalkylated to reduce foam in a fermentation broth.
U.S. Pat. No. 6,083,998 concerns defoamer compositions for alcoholic fermentations which as aqueous based and comprise polydimethylsiloxane oils, ethylene oxide/propylene oxide block copolymers and a silicone/silica blend.
When producing ethanol from readily fermentable sugar materials, such as sugar cane juice and molasses, foam generated by the fermenting organism is a serious problem.
Even though chemical defoamers can be used there is still a desire and need for providing processes for producing fermentation products, such as ethanol, where the foam generation is reduced/controlled.